Telephone-exchange system.



E. R. CORWIN. TELEPHONE EXCHANGE SYSTEM.' APPLICATION FILED DEO. 142, 1904.

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UNITE STATS PATENT OFFICE@ ELMER R. CORWIN, OF CHICAGO, ILLINOIS, ASSIGNOR TO MONARCH TELEPHONE MANUFAC- TURING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Nov. 3, 1908.

Application filed December 12, 1904. Serial No. 236,593.

'o all whom fit may concern:

Be it known that I, ELMER R. Con'WIN, a citizen. of the United States of America, and a resident ol' Chicago, county of Cook, and State of Illinois, have invented a new and uselul Improvement in a Telephone EX- change System, of which the following is a speciiicatien.

My invention relates to that class of telephone exchange systems in which a central source, or central sources, of energy supplies the lines with current for the operation of the signals, and, it desired, for the operation of the transmitters as well, and has for its general object the simplification ci the wiring' of the central oi'lice switchboard by limiting the number of conductors required to be carried through the multiple jacks to the otherwise necessary pair of limbs et' the line, and also has as an obiect a similar limiting of the 'flexible cords to a single pair without auxiliary signal strands, with the attendant -advantage ci requiring but two conductors to appear in the plug ier registry with a similar number of electrical parts in each of the jacks. The advantages of this economizing in the parts of the structure of the switchboard and the consequent investment, and those ci increased economy in maintenance, and ci the more limited number of cord and plug conductors to be maintained, are well known to those skilled in the art. In my invention these advantages are gained, together with those of reliability of signals and the preservation of an electrical balance of the line. i

My invention is illustrated in the accompanying drawing, which shows the circuits ci a cord circuit and operators telephone circuit, and two line circuits adapted to be con-- nected together by cord circuits of the type shown.

Referring to the drawing, 1 and 2 are the substation telephones of two ci the lines, these may be of any type suitable for use with a systeml having` signals operated on the central energy plan, the important requirem ents being th at when the receiver at the station is en its hook, the circuit of the instrunient is opened to direct current, although closed te alternatine,` current for the operation ci the. signal bell. lf there be no necessity c a signal hell, as is true in equipments for outgoing service only, the circuits of the telephone may be truly open to all currents except in times of use. lil/'hen the receiver is not on the hook, a path' for direct current is provided through the instrument. It the system is to be adapted for a central energy supply of current for the transmitters at the substations, no local battery will be required although such a substation circuit as would use a local battery might be adapted for use with my system without sacrificing any of the advantages of automatic control of central oflice signals.

3 and 4 are the limbs ol one ol the lines, and 32L and 4a, those of the other. As the two lines illustrated are quite identical, first particular reference will be made in this description to that which is shown at the left oil the sheet. It is this line which is considered as originating a call, and the other as receiving a call. The parts 5 and 6, 5al and 6a, respectively, compose two ol the spring jacks associated with the line formed ol the limbs, 8 and 4. The parts 5 and 5a, respectively, are the test bushings usual in spring jacks, and are adapted to make contact with the sleeves, as 7, oi' such plugs as are indicated as a whole by 9. The tip, 8, of such plug 'will register with the spring, 6, ol' a jack. The relay, 10, is permanently connected to the limb, 3, of the line, and the other terminal ol' its winding to the live pole olI the battery, B. If the subscriber at station, I, removes his telephone i'rom its hook, current will ilow from the battery, B, through the relay, l0, over the limb, 3, of the line, tln'ough the telephone instrument, to the central oliice over the limb, 4, of the line, through the contact between the armature, ll, and the back contact, l2, ol' the relay, 13, and thus to ground. The result will be the actuation ol' the armature, lll, of the relay, l0, making contact, l5. As the armature, lo, ol the relay, 13, is upon its back contact, 17, current will now low from the battery, B, through these contacts and the lamp, 18, to ground. rlhe lamp, IS, being adapted to give a visible signal at the potential of the battery, B, it will now do so, notifying' the operator that a call upon the line in question requires to be answered, and the lamp, 18, will remain so displaying a signal until the call is answered, or until the subscriber has returned his receiver to its hook. Upon the answering of the signal by the insertion ol the plug, 9, in, say, the j ack formed of parts 5 and 6, current will llow'from the battery, B, through the relay, 13, over the wire, 19, by contact of the test bushing, 5, to the sleeve, 7, of the plug, 9, then through the winding o'l the relay, 20, to ground. But the winding oi'l the relay, 20, is of turns and resistance relatively few and low with relation to those composing the winding of the relay, 13 5 it is a consequence that the current which flows through these relays, 13 and 20, in series, is ample to energize the former, moving both its armatures, 11 and 16, but not moving the armature, 21, of the relay, 20. Four results, one passive and three active, come 'from these conditions:

First: The circuit oi' the lamp, 18, is interrupted by breaking of contact between the armature, 16, and its point, 17, thus eliacing the signal as is necessary.

Second: The making of contact between the armature, 11, and its point, 22, connects the test bushings, 5 and 5a, through conductor, 19, with the limb, 4, of the line. It will be observed that this condition with reierence to the limb, 4, has not bei'ore existed, nor have the test bushings been before connected to that limb of the line except over another and longer path.

Third: As the armature, 21, of the relay, 20, is not moved, the supervisory signal lamp, 23, has its circuit lei't open which leaves the lamp in condition oi' darkness, to indicate to the operator that the subscriber is at his telephone.

Fourth: Whereas the test bushings, 5 and 5a, had during a time oi no connection of a plug with one oi them, a potential with reference to the earth quite the same as that of the live pole of the battery, there is now such a potential with reference to the earth at these test bushings as is controlled by the drop of potential through the winding of the relay, 20; and this change of the electrical condition of the test bushings 5 and 5, and such others as may be connected with the line in question, may enable a busy test to be made on the line if occasion shall require.

Actuating the listening key designated as a whole, 24, the operator connects her telephone circuit with the limbs o'l' the cord circuit, and therefore with the limbs of the line. The operators telephone circuit is quite as usual except with reference to the winding, 25, the spring, 26, and the contact, 27, all oi' which have to do with busy test l'unctions, and will be described later. Having learned from the calling subscriber what line it is that he desires, the plug designated as a whole, 28, (being the plug of the air particularly intended for calling,) wil be selected by the operator, and its tip, 29, touched against the test bushing of the called line. Either a click will be heard, indicating that that line is in use, or none will be heard, indicating that it is free. The latter will be true and 'the line may be taken if the test bushings have the same potential as the live pole of the battery, which in turn will be true unless some plug, electrically similar in circuit to plugs, 9 and 28, is in a jack of that line. li' the latter is true, the test potential o1' the bushings will be somewhat less than that of the live pole of the battery, and a click will be received by the operator for the following reason:

The tip, 29, of the plug with which the test is made has a circuit through the ringing key, 31, of usual and standard type, directly to the contact, 27. This is individual to the particular listening key of the cord circuit in use. As the listenin@` key, 24, is still actuated since receiving tie called number from the calling subscriber, the spring, 26, will be in contact with the point, 27. Other listening keys of the group of cord circuits used by the operator, have similar springs to 26, and these springs of a given operators equipment are all connected together and to one of the terminals of the winding, 25, of an induction coil associated with the operators telephone.4 The other terminal ol that winding, which is neither the usual primary nor secondary winding, but which we may call the tertiary winding, is connected to the live pole of the battery, B. This tertiary circuit is of quite high resistance. At the time of its contact, therefore, current will iiow from the battery, B, through the winding, 25, and contact of spring, 26, with point, 27, through the ringing key, 31, to the tip, 29; and if there is a connection of some other plug with another jack of that line, current will low over the test bushing touched, as for example, l32, and over the wire, 33, to that test bushing of the busy line in which exists the plug which is making the line busy. This may be considered to be 34. From this oint, as 34, current will further flow to the sleeve of that distant plug, through the distant ringing key similar to 31, through the distant supervisory relay oi that distant cord circuit similar to 35, and thus to ground. As current is still iiowing through that distant relay, similar to 35, there will be a potential somewhat less than that of the live pole of the battery, and the current impulses thus resulting by induction in the secondary winding ot the induction coil of the testing operators telephone set, will produce the necessary click in the operators receiver.

Assuming that no click is heard, and that the line is taken by the operator, a registry of contacts similar to that described with reference to the calling subscribers line will enable ringing current to pass from the generator, 36, and the tip, 29, oi the plug, 28, to

the wire, 3a, of the line, through the ringer, 7

' which wi bell does not result in his response, the relay, 41, will not be energized, and its armature, 42, and oint, 43, will establish a circuit be seen to shunt the winding of the relay, 44, by the mere resistance of the connecting wires; the relay, 44, is thus prevented from operating, which it would do in series with the supervisory relay, 35, of the circuit if it were not for this short circuiting. The relay, 35, is therefore in series with but negligible resistance and the battery, B. As it is similar to the relay, 20, described as having few turns and low resistance, the relay, 35, will be energized under these conditions in a sufficient degree to operate and will close its armature, 45, upon the contact, 46. This in turn will place the lamp, 47, in shunt with the winding of the relay, 35, in which condition, with a practical proportion of values which I will describe later, the lamp, 47 will be illuminated. The signal thus given is of the meaning to the operator that the subscriber being called has not replied, and she will either' continue to vring his bell, or will in time notify the calling subscriber that he does not respond.

Vhen the called subscriber does respond, the relay, 41, is energized quite as was true with the relay, 10, in the described originating call. The breaking of contact between 42 and 43, not only so far decreases the current through the relay, 35, in such a degree as to cause its armature to fall away, extinguishing the lamp, 47, but by the operation of the relay, 44, extends the limb, 43, of the called line through the armature, 39, and the contact, 43, to the conductor, 33, the bushing, 32, and the sleeve, 30, of the calling plug, 28. Conversation may now ensue. But for the breaking of contact between the other armature, 49, and its point, 50, the line lamp, 51, of the calling line, would have been lighted, which would have given al signal, falsely indicating an originating call. This will not occur, and for the reasons stated. As the relays, 20 and 35, during the progress of conversation, are receiving insuflicient current to operate, their associated lamps will remain dark. Upon the completion of the conversation and the hanging up of the telephone receivers by both of the subscribers, or by either of them, the corresponding relay, 10 or 41, will allow its armature to be released. This will restore contacts which I have described before, shunting the windings of the relays, 13 or 44, increasing the current through the corresponding supervisory relay, 20, or 35, bringing the associated lamp, 23 or 47, again into action, indicating that the connection requires attention, this being the withdrawal of both plugs if both lamps are illuminated. So far as the signals are concerned, their behavior is quite as is common in generalpractice at this time.

ln order that the consequences of operations may be as l have Ddescribed, l find that in practice the resistances of the various relays and signals which are likely to have inter-relations are practical when they are about as follows: lf the potential of the battery, B, is approximately 40 volts, the relay, 13, may have a resistance of 2000 ohms, and the relay, 20, of about 20() ohms, accomplishing the result of operating or not operating as l have described. These are merely suggested practical values; as, due to the inechanical and magnetic dimensions of the supervisory relays, considerable variation .3. ay he made from the values I have assigned without at all effecting the results to be achieved. As the supervisory lamps are only placed in shunt with their controlling relays at a time when the entire resistance of the relays,o 13 and 44, is shunted, the drop of potential across the lamp terminals is therefore the entire voltage of the battery, or very near to that. 1With a 40 volt source of energy, therefore, 40 volt lamps are practical for supervisory purposes.

During conversation, current is supplied to the subscribers telephone through the line relay and supervisory relay, each in series with one of the line conductors. These relays, in the case of the line to the station, l, in the drawing, would be respectively those designated as 1() and 20. lt will be reine-inbered that during actual conversation, the relay, 20, is not energized by suflicient current to draw up its arm ature, 21, and therefore the inductance of that part of the circuit is not diminished by the non inductive shunt constituted by the lamp, 23.

The condensers, 54 and 55, serve the purpo se of transmitting voice currents with ease, and at the saine time preventing false signals due to the operation of the supervisory signal associated with the answering cord by any motions of the hook of the telephone on the called line. individuality of signals is thus retained.

it will be seen that the operation of the supervisory signal lamps, 23 and 47, depends, with the particular arrangement which l have shown, upon the current through the lamp, as well as upon the presence of a sufliciently low resistance in series with the lamp to enable it to secure suflicient current. For instance, in the case of the lamp, 23, associated with the answering cord, if the contact of the armature, 21, with the relay, 20, were not made upon its point, there would be no circuit for current through the lamp, 23. But if this contact were made and by accident or design remained closed, the super isory signal would still be operative and responsive to the necessary inotions of the hook switch at the calling subscribers station 5 and this is for the reason that when the subscribers telephone existence of a path for receiver is upon the hook, the contact of the armature, 14, with its normal point, is not broken, and the resistance of the relay, 13, is effectively shunted from being in series with the lamp, 23. Il the subscribers receiver were oil' the hook, the relay, 10, would be energized and the contact shunting the relay, 13, would be broken. So great a resistance as I have assigned to the relay, 13, would eiliectively prevent the glowing of the lamp, 23, il. the latter is adapted to give a practical signal on the full voltage of the battery. I desire, therefore, to have this explanation of my invention understood to point out that with proper and feasible proportion of parts, the supervisory signal system may be made operative on either of the plans which I have described. as involving the relations of the supervisory lamp, 23, the circuits by which it is controlled, and in which it operates.

I do not wish to be limited to the usevof supervisory relays in practicing all features of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is,

1, In a telephone system, a telephone line, a source o'll current, a relay permanently in series with said source of current and one limb of said line, two-conductor spring jacks having one conductor of each permanently connected to the limb ol said line containing said relay and the other conductor of each normally disconnected 'from the remaining limb of said line, a relay adapted when energized to connect the remaining limb of said line to the conductors of said spring jacks not normally connected to that line, a signal lamp adapted to be operated by the operation of said series relay, and a shunt path about the other said relay adapted to be broken when said series relay is energized, substantially as described.

2. In a telephone system, a line ol' two limbs, a spring jack of two members, a conductor permanently connected between one limb oisaid line and one member of said spring jack, a cut-oli relay, a line relay, line relay contacts normally shunting said cutofl relay, and means ada ted to break the shunt 'from said cut-ofil re ay and to connect the other limb of said line immediately to said spring jack during conversation over said line, substantially as described.

3. In a telephone system, a telephone line of two limbs, a spring j acl; ol? two conductors, a cord circuit oil two strands, a line re lay normally in series with one limb of said line, a cut-off relay normally short circuited by contacts of said line relay, a source oi current having one pole permanently connected to both said relays, supervisory relays permanently in bridge between one strand of said cord circuit and the other pole of said source of current, and means adapted to place said cut-oli relay and one of said su'- pervisory relays in series with each other and the source ol current without operating said supervisory relay, substantially as described.

4. In a telephone line, a source of current, a line relay, a cut-oil relay normally short circuited by contacts of said line relay, a two-strand cord circuit, a supervisory relay bridged between one strand of said cord circuit and one pole of said source of current, spring jacks connected to said telephone line, plugs connected to said cord circuit, means adapted by a connection of one of said plugs with one of said spring jacks to operate the armature of a corres onding one o'l' said supervisory relays whi e the short circuit of said cut-off relay continues, and to release it when the short circuit is broken, and means adapted to energize said cut-off relay when the short circuit is broken, substantially as described.

5. In a telephone system, a source o'l current, a supervisory relay having one winding and adapted not to attract its armature during conversation, said source and said winde ing being in series with each other and with the line limbs and sub-station tele hone g a supervisory lamp in a circuit norma ly o en, and line controlled means adapted to p ace said lamp in shunt with said relay when said relay is energized to attract its armature, substantially as described.

6. In a telephone system, a source ol current, a two-strand-cord circuit, a supervisory relay having one winding, said source and said winding being in series with each other and with th'e line limbs and sub-station telephone; a supervisory lamp in a circuit normally open, line controlled means adapted to place said lamp in shunt with said relay when said relay is energized, and means adapted not to energize said relay when the receiver of a' connected sub-station telephone is off the hook and to energize said relay when the receiver of a connected substation telephone is on the hook, substantially as described.

' 7. In a telephone system, a source of current, a supervisory relay adapted not to attract its armature during conversation, a supervisory lamp, line controlled means adapted to place said supervisory lamp in shunt with said relay when said relay is energized, and a circuit including said source of current, said relay, the limbs oi a connected telephone line and a substation telephone and adapted to' furnish to the substation telephone energy for speech transmission, substantially as described.

8. In a telephone system, a source of current, a supervisory relay having a single winding, a supervisory lamp placed in shunt with the winding of said relay by the contacts of said relay when said relay is energized, a substation telephone having a hook switch, a circuit closed during conversation including said source of current7 said relay `and Said hook switch, and line controlled relay in shunt then being in series With jack and line relay Contacts severable by disconneotion of the plug from 'the jack.

Signed by nie at Chicago, county oi' Cook, State of Illinois, in the presence of two Witnesses.

ELMER R. CORWIN.

Witnesses z HAZAEL C. PRADO, EVA A. GARLooK. 

